Injury to the anterior cruciate ligament (ACL) results in a threat to an active lifestyle and exposes the patient to risk of early osteoarthritis. ACL reconstruction is typically chosen by individuals to allow a return to their previous work and sports activities. The results of primary ACL reconstruction have in general been good at restoring functional stability, but patients' long-term outcome remains unknown. The Multicenter Orthopaedic Outcomes Network (MOON) is an established consortium designed to enroll and longitudinally follow a population cohort of ACL reconstructed patients to determine the modifiable predictors (or risk factors) of long-term outcomes of ACL reconstruction in order to establish patient-specific predictive models of clinically important outcomes. The objective of this prospective multicenter cohort of ACL reconstructions is to identify both the long-term prognosis and the potentially modifiable predictors of symptoms of osteoarthritis (OA), sports function, activity and general health through validated patient- reported outcomes, and incidence of ACL reconstruction graft and/or contralateral ACL failures. Our initial grant (R01 AR053684) allowed us to enroll over 2,300 patients and obtain both 2 and 6 year follow-up on this cohort. At both time points, we have been able to obtain a minimum of 85% follow-up using validated patient-reported outcome questionnaires and 93% via phone follow-up. Two of the original three Aims from the parent grant will be advanced in this competitive revision, 1) validated patient-reported outcomes of sports function, activity level, general health, and symptomatic OA, and 2) ACL graft or contralateral ACL failures. The objective of this revision is to complete 6 year follow-up on an additional unfunded MOON cohort of 1251 ACL reconstructed patients (with an already completed 86% 2 year follow-up rate) in the last 1.5 years of the parent grant (4/2014 - 8/2015). This would increase our existing sample size by ~ 50%, and would enable us to build the most comprehensive personalized models to address detailed contributions of meniscus and articular cartilage injury and treatment (and their interactions) to several patient reported outcomes and OA symptoms. Furthermore, we would be the first to perform complex multivariable predictive modeling of ACL graft and contralateral ACL failure. The additional variables incorporated into longer 6 year time interval is particularly important for establishing the longer-term outcomes and symptoms of OA and incidence of both ipsilateral and contralateral ACL tears.